I use single 4" Merrill drivers in my Zigmahornets. I would never think of doubling or quadrupling these. The imaging is amazing and you won't get that with multiple drivers, just more sound. Most single drivers tend to be very efficient with power.
The lack of a crossover is very clearly a benefit with this design.
Another option would be a coax driver to maintain the absolute best imaging (in my opion). Seas makes a wonderful 6" coax that can be biamped/biwired or single wired with a jumper. The crossover is absolutely minimal in their design. Not a cheap option but amazing sound.